Recent wireless communication systems can wirelessly transmit/receive data in a wireless terminal at a high data transmission rate, while the wireless terminal is in motion. The wireless communication systems use repeaters to connect wireless terminals in shade regions to base stations.
The wireless communication systems use the same frequency band in a forward channel (from a base station to a wireless terminal) and a reverse channel (from a wireless terminal and a base station). The wireless communication systems use a Time Division Duplexing (TDD) method that distributes the forward and reverse channels according to time. Therefore, repeaters should perform link route switching at an exact time point.
In general, frames are synchronized in an Orthogonal Frequency Division Multiple access (OFDMA) system by using a method using correlation in a cyclic prefix (CP) duration, a method using correlation in a preamble duration, or a pilot pattern detecting method.
All the methods can be used to synchronize the link routes of TDD repeaters. However, when the pilot pattern detecting method is used, the TDD repeaters require a demodulator. Since the use of a demodulator adds up to complexity and costs of the wireless communication system systems, it is not efficient to use the pilot pattern detecting method. Therefore, the methods using a CP duration and a preamble duration may be used.
When the method using a CP duration or a preamble duration is used to synchronize the link routes of the TDD repeaters, the level of correlation values may fluctuate deeply due to the characteristics of a wireless channel. Therefore, there is a problem that signal processing should be performed additionally to keep the correlation value at a uniform level.
Also, when the method using a CP duration or a preamble duration is used to synchronize the link routes of the TDD repeaters, the starting and termination time points of a downlink may be known accurately. However, since an uplink termination time point is obtained from calculation based on a ratio of TTG to the downlink, there is a problem that a switching time offset may occur unintentionally when an RF repeater switches its link route into a downlink.